Want to grow bigger blueberries? Make your bees work harder

If your berries aren't big enough this year, you might want to fire your
bees and take on some that work harder.

That's the advice from Margriet Dogterom, a PhD student in biological sciences,
who is investigating bees' work habits in blueberry fields in a study that's
the first of its kind.

She wants to know whether some species of bees are busier than others when
it comes to pollinating flowers. The humble honeybee, the farmer's favorite,
is a laggard, she says, compared to bumblebees or Mason bees, both of which,
on a per bee basis, drop more pollen onto flowers.
More pollen produces berries that are half again as big, and ripen almost
a week earlier, she says.

Bees pollinate flowers accidentally while gathering nectar in the spring.
Pollen grains from the
anther on one bloom get snagged on a bee's hairy legs and are rubbed off
on the stigma on the next bloom the bee visits. This fertilization is what's
needed for a bumper summer crop.

Dogterom is the first researcher to analyze how many individual pollen grains
are transferred by different species of bees. Each time a bee visits a flower,
she carefully counts the number of grains it leaves behind. Bumblebees drop
huge amounts, she found, about 70 grains per visit. Mason bees leave about
55 grains and honeybees only 40.

Extra efforts on the part of bees paid off in berry size. Blooms which received
less than 25 grains of pollen produced berries just over one gram in weight.
When 125 grains of pollen were dropped, blueberries grew bigger by more
than a third, topping 1.7 grams a berry. "They looked
like grapes, they were so big," Dogterom says.

But how to ensure a pollen drop of that amount? The bumblebee is a clear
contender at 70 grains, but each flower would need at least two visits from
even a bumblebee. The answer might be to combine bee species, bumblebees
and honeybees, for example, Dogterom says, a visit from each species ensuring
the 125-grain magic number.

Larger pollen drops also resulted in shorter ripening time, she found. When
125 grains or more of pollen were deposited, ripening time dropped to 58
days from 64. An earlier berry crop means more money for the berry grower,
Dogterom says.

Now in her third year of her PhD research, Dogterom hopes to finish up next
year, her third growing season. "I'm trying to get to the bottom of
it all," says the former bee inspector who is carrying out her field
work on a Coquitlam farm.

Her research comes at a critical time for berry and orchard growers. Over
the last five years, mites have wiped out wild honeybees in Canada. Honeybees
in managed colonies have survived only because beekeepers regularly treat
them for mites. But for the first time, farmers are faced with the prospect
of a shortage of honeybees when they need them, during the three to four
crucial weeks of pollination. "It's a problem bee keepers are struggling
with," Dogterom says.

The difficulty with switching immediately to another species, such as bumblebees
or Mason bees, is that those colonies are small, containing only two or
three hundred bees.

"That's not enough to take care of acres of blueberries," Dogterom
explains. Producing more colonies of bees is a lengthy, time-consuming and
costly process. "It comes down to economics," she says. "Small
berry growers and orchardists are dependent on the sometimes scarce resource
of honey bee colonies until other bees are both available and economical
to buy or rent."